The psychomotor stimulants amphetamine (AMPH) and methylphenidate (Ritalin) are used clinically in the treatment of narcolepsy, fatigue, obesity, and childhood hyperactivity syndrome. In addition to these clinical uses there is widespread illicit abuse of psychomotor stimulants for recreational purpose, and to enhance performance when sustained alertness is required over a long period of time. The experiments proposed in this application will investigate the basic mechanism(s) by which these drugs act in the brain to produce their behavioral and cognitive effects. The psychomotor stimulants are thought to produce their behavioral effects by stimulating the release of dopamine (DA) from the striatum and nucleus accumbens. However, the mechanisms by which these related compounds induce DA release may be different. It has been suggested that AMPH releases DA from a newly synthesized nonvesicular DA pool, whereas methylphenidate and a related drug, amfonelic acid (AFA), are believed to induce DA release from synaptic vesicles. In order to directly test the hypothesis that these drugs act to release DA from different subcellular compartments, it is necessary to first develop a method with which to dissociate the release of newly synthesized nonvesicular DA from vesicular DA release. Preliminary experiments have demonstrated that following the incubation of striatal tissue with [3H]DA or [3H]tyrosine, a superfusion system can be used to study the simultaneous release of (1) endogenous DA and (2) preloaded [3H]DA or [3H]DA synthesized from [3H]tyrosine. The purpose of the experiments proposed is two-fold. The initial series of experiments will characterize the differences between the release of endogenous DA, preloaded [3H]DA, and [3H]DA synthesized from preloaded [3H]tyrosine from striatal tissue in vitro. Dopamine release will be stimulated with AMPH, methylphenidate, AFA, and KC1. In the second series of experiments the hypothesis that methylphenidate and AFA release DA from vesicular stores, whereas AMPH preferentially releases DA from a newly synthesized nonvesicular pool will be directly tested.